In order to machine parts to close tolerances it is desirable to provide built-in automatic adjustment means for changing the position of a cutting tool with respect to the workpiece. In the case of boring cutters one approach has been to connect the cutting tool on a cutting bar connected to the outboard end of a spindle shaft. The spindle shaft has a hollow configuration and an actuating rod for the mechanism is directed through the hollow shaft to vary the position of the cutting tool following a boring operation to avoid tool drag marks on the surface of a bore finished by the cutting tool.
An example of such a machine tool is set forth in U.S. Pat. No. 3,740,161 where the adjustment means is located in a housing mounted on a machine table separately from the spindle housing. In such cases the spindle housing must be assembled as a separate unit; the adjustment means is separately assembled and then the individual pieces must be separately assembled on the machine base. Such units, if replaced separately require different craftsmen and depending upon plant classification systems may require electricians, millwrights, machinists and/or riggers to make changes or repairs to the assembly.
Furthermore, the use of a separate spindle, a separate drive motor and a separate adjustment mechanism require drive train arrangements which will direct substantial lateral loadings on bearing components in the adjustment mechanism which overtime can cause excessive wear therein. In the case of the '161 patent parts of the adjustment mechanism are isolated from the spindle drive by use of flexible couplings but the bearings which support the actuating rod for rotation concurrently with the rotation of the spindle shaft are located so as to be subject to some transverse or lateral loading unless the component parts are very precisely aligned coaxially. Such alignment is difficult to achieve under field installation, repair and replacement circumstances.